In Fibre Channel networks there are a plurality of switches that are used to switch Fibre Channel traffic between various destinations, e.g., servers and storage devices. In a given Fibre Channel network or Fabric, one switch among the plurality of switches is selected to serve as the so-called Principal Switch. The Principal Switch is mainly responsible for assigning unique domain identifiers to all the switches in a Fabric.
The decision about which switch in a Fabric is to serve as the Principal Switch can be forced by a network administrator, or the switches can be left to decide for themselves using built-in logic, during what is called a Principal Switch Selection phase. The switch that is serving as the Principal Switch also is responsible for assigning unique domains to itself and the other switches in the Fabric during the Domain Identifier (ID) Distribution phase.